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The Multijunction (MJ) monolithic approach is very attractive for a competitive concentrating photovoltaic (CPV) technology; it has been successfully applied for InGaP/GaInAs/Ge triple-junction structures but it is more difficult to be exploited for manufacturing 4-junction solar cells, in particular when III-V and IV elements are both used. So far, the integration of the 1 eV SiGeSn material in the lattice-matched InGaP/GaInAs/Ge triple-junction structure has required the utilization of two different growth apparatus, nearly losing the economic advantage of the monolithic architecture, owing to the related higher capital expenditure. The central technical challenge for realizing InGaP/GaInAs/SiGeSn/Ge solar cell at low cost, with an industrial approach, lies in the growth of III-V and IV elements in the same MOVPE equipment, by solving the "cross contamination" problem among the III-V elements and the IV elements. In this contribution, for the first time, the results of the investigation concerning the growth of SiGe(Sn) and III-V compounds in the same MOVPE growth chamber are presented. The epitaxial layers have been characterized by XRD, SEM, TEM, EDX, SIMS and ECV profiling. It is eventually shown that by starting from a modification of the MOVPE equipment and by setting up proper growth condition the contamination of III-V elements in IV based materials can be drastically reduced from 1020 cm-3 to 2*1017 cm-3, while the contamination of IV elements in III-V compounds can be reduced from 4-5*1017 cm-3 to 6*1016 - 3*1014 cm-3 depending on the substrate used. [ABSTRACT FROM AUTHOR]

It is presented the optical design of a mirror based solar concentrator operating at concentrating factors higher than 850suns with an optical efficiency greater than 83% and an angular acceptance of at least ±0.5°. The optical system consists of an off-axis primary mirror optimized to work in conjunction with a secondary optical element which homogenizes the light on the photovoltaic (PV) cell and also increases the acceptance angle of the solar concentrator. Since in a high concentrating system the collected optical radiation can impinge on the PV cell also at high incidence angles, during the optical design and optimization particular attention was paid to reduce the number of rays impinging on the PVcell at high incidence angle. Furthermore the angular response of the PV cell was included to calculate the efficiency value of the whole system and to calculate the spatial distribution of the photocurrent in the different subcells constituting the multi-junction solar cell. [ABSTRACT FROM AUTHOR]